1. Field of the Invention
This invention relates to a navigation apparatus, a method for map matching performed in the navigation apparatus, and a computer-readable medium storing a program for executing the method.
2. Description of the Prior Art
Conventional navigation apparatuses are capable of computing recommended routes based on destination data established by a user (e.g., driver) and vehicle information such as vehicle speed, the current position of the vehicle and the like. Further, the conventional navigation apparatuses are capable of displaying the computed recommended routes on a screen to provide route guidance to the user..
Further, the conventional navigation apparatuses are also capable of carrying out a map matching process. In this map matching process, first the conventional navigation apparatus compares the xe2x80x9cshapexe2x80x9d of a vehicle""s route that the vehicle has passed to the xe2x80x9cactual road layout.xe2x80x9d Then, the navigation apparatus xe2x80x9cmatchesxe2x80x9d the vehicle""s actual location on the road to its position on a digital road map on the screen.
Furthermore, the conventional navigation apparatuses are also capable of carrying out a corner control operation. In this corner control operation, the conventional navigation apparatus automatically shifts down into a low-speed transmission gear when the vehicle approaches a corner, so that the vehicle can turn the corner with low speed sufficient for passing the corner safely.
Hereinafter, problems involved in the conventional navigation apparatuses are described with reference to FIG. 4. In FIG. 4, a freeway 50 has a main way 51 and an off-ramp (branch way) 52 which branches off at a fork. As shown in this figure, within the distance xe2x80x9cDxe2x80x9d indicated by the arrow, the off-ramp 52 is xe2x80x9cgraduallyxe2x80x9d away from the main way 51 according as the off-ramp 52 extends.
When the vehicle having such a conventional navigation apparatus has entered the off-ramp 52 to drive off the freeway 50, it is impossible for the conventional navigation apparatus to know the exact location of the vehicle until the vehicle reaches a position where the off-ramp 52 is far enough away from the main way 51. In other words, it is impossible for the conventional navigation apparatus to properly judge whether the road on which the vehicle is actually traveling is the main way 51 or the off-ramp 52 until the vehicle reaches a position where the off-ramp 52 is far enough away from the main way 51. This is because the shape and position of the main way 51 within the distance D is very similar to those of the off-ramp 52 within the distance D, and therefore the conventional navigation apparatus cannot properly carry out the above-mentioned map matching process.
Therefore, when the vehicle having the conventional navigation apparatus enters the off-ramp 52 from the main way 51, there is a possibility that the following problems occur.
First, since the conventional navigation apparatus cannot exactly determine the road on which the vehicle is traveling just after passing the fork, there is a possibility that the vehicle""s location is displayed at a wrong position on a digital road map on the screen for a while after passing the fork.
Second, even when the vehicle has inadvertently entered the off-ramp 52 from the main way 51, the conventional navigation apparatus cannot compute a new recommended route just after passing the fork. This is because the conventional navigation apparatus cannot properly know its current position until the vehicle is far enough away from the main way 51. Therefore, in such a case, the conventional navigation apparatus cannot provide information as to a new recommended route just after passing the fork.
On the other hand, when the vehicle having the conventional navigation apparatus travels straight on the main way 51 without entering the branch way 52, there is a possibility that the following problem occurs. Namely, when the vehicle travels straight on the main way 51, there is a possibility the conventional navigation apparatus misjudges that the vehicle has entered the branch way 52. This is because the shape and position of the main way 51 within the distance D is very similar to those of the branch way 52 within the distance D, and therefore the navigation apparatus cannot properly carry out the map matching process. Accordingly, in the case where the conventional navigation apparatus has made such a misjudgment, the navigation apparatus judges there is a corner 53 in front of the vehicle, although the vehicle is actually traveling on the main way 51. In such a case, the navigation apparatus carries out the corner control operation to reduce the speed of the vehicle, thus leading to the possibility of a car clash.
In view of the above, it is an object of the present invention to provide a navigation apparatus which makes it possible to properly carry out the map matching process to determine the road on which a vehicle is traveling just after passing a fork or on which the vehicle is traveling just after passing the fork.
Further, it is another object of the present invention to provide a method for the map matching performed in the navigation apparatus.
Furthermore, it is other object of the present invention to provide a computer-readable medium storing a program for executing the method for the map matching performed in the navigation apparatus.
In order to achieve the above objects, the present invention is directed to a navigation apparatus which is mounted on a vehicle, the navigation apparatus being capable of displaying a vehicle""s location on a digital road map on a screen to provide route guidance to a user of the vehicle, the apparatus comprising:
current position detecting means for detecting a current position of the vehicle;
a database which stores route/map data including at least information of forks in roads, in which the fork information of each of the forks is stored in association with at least two predetermined conditions relating to features of the fork;
imaging means for taking images of a road on which the vehicle is traveling;
means for detecting and monitoring lane markers on the road to obtain detection results, the detection and monitoring being performed by processing the images taken by the imaging means;
first judging means for judging whether or not a fork is located ahead of the current position of the vehicle, the judgment being made based on the route/map data;
retrieval means for retrieving the fork information of the fork from the route/map data, the retrieval being made in a case where the first judging means judges that a fork is located ahead of the current position of the vehicle;
second judging means for judging whether or not the vehicle has entered a specific area that is set with respect to the fork; and
road determining means for determining the road on which the vehicle is traveling after passing the fork or on which the vehicle is going to travel after passing the fork, the determination being made based on the detection results and the predetermined conditions relating to the fork.
According to the present invention described above, it is possible for the navigation apparatus to know the road on which the vehicle is traveling just after passing the specific fork (or, on which the vehicle is going to travel just after passing the specific fork), based on the road determination result. Further, when the vehicle""s actual location is displayed at a wrong position on the digital road map, the navigation apparatus can correct the position so that the road on which the vehicle is actually traveling immediately after passing the fork just corresponds to the road image along which the vehicle""s mark is moving on the digital road map. This is advantageous in the following points. Namely, the driver can know its accurate location from the displayed information on the screen immediately after passing the specific fork.
In this invention, it is preferable that the navigation apparatus further comprises third judging means for judging whether or not the vehicle has left the specific area, wherein the road determining means includes (i) first means for making the determination when the vehicle is within the specific area; and (ii) second means for making the determination in a case where the third judging means judges that the vehicle has left the specific area. In this case, it is preferable that the predetermined conditions include first and second conditions, in which the first means makes the determination based on the first condition and the detection results obtained when the vehicle is within the specific area, and the second means makes the determination based on the second condition and the detection results obtained when the vehicle is within the specific area. Further, it is also preferable that the navigation apparatus further comprises fourth judging means for judging whether or not the first means has successfully determined the road, wherein the second means makes the determination in a case where the fourth judging means judges that the first means has not successfully determined the road.
Further, in this invention, it is also preferable that the detection and monitoring means detects the type of each of the lane markers while monitoring lane change performed by the vehicle.
Furthermore, in this invention, it is also preferable that the navigation apparatus further comprises correcting means for correcting the vehicle""s position displayed on the digital road map based on the determined road to match the vehicle""s location on the road to its position on the digital road map.
Another aspect of the present invention is directed a method for map matching performed in a navigation apparatus mounted on a vehicle, the navigation apparatus being capable of displaying a vehicle""s location on a digital road map on a screen and matching the vehicle""s location on a road to its position on the digital road map, the method comprising the steps of:
(a) detecting a current position of the vehicle;
(b) taking images of a road on which the vehicle is traveling;
(c) detecting and watching lane markers on the road to obtain detection results, the detecting and watching being performed by processing the images taken at the step (b);
(d) judging whether or not a fork is located ahead of the current position of the vehicle based on route/map data stored in a database of the navigation apparatus, the route/map data including at least information of forks in roads, in which the fork information of each of the forks is stored in association with at least two predetermined conditions relating to features of the fork;
(e) retrieving the fork information of the fork from the route/map data in the database, the retrieval being made in a case where it is judged at the step (d) that a fork is located ahead of the current position of the vehicle;
(f) judging whether or not the vehicle has entered a specific area that is set with respect to the fork;
(g) determining the road on which the vehicle is traveling after passing the fork or on which the vehicle is going to travel after passing the fork, the determination being made based on the detection results and the predetermined conditions relating to the fork; and
(h) correcting the vehicle""s position displayed on the digital road map based on the determined road to match the vehicle""s location on the road to its position on the digital road map.
Further, another aspect of the present invention is directed a computer-readable medium which stores a program for executing a method for map matching performed in a navigation apparatus mounted on a vehicle, the navigation apparatus being capable of displaying a vehicle""s location on a digital road map on a screen and matching the vehicle""s location on a road to its position on the digital road map, the method comprising the steps of:
(a) detecting a current position of the vehicle;
(b) taking images of a road on which the vehicle is traveling;
(c) detecting and watching lane markers on the road to obtain detection results, the detecting and watching being performed by processing the images taken at the step (b);
(d) judging whether or not a fork is located ahead of the current position of the vehicle based on route/map data stored in a database of the navigation apparatus, the route/map data including at least information of forks in roads, in which the fork information of each of the forks is stored in association with at least two predetermined conditions relating to features of the fork;
(e) retrieving the fork information of the fork from the route/map data in the database, the retrieval being made in a case where it is judged at the step (d) that a fork is located ahead of the current position of the vehicle;
(f) judging whether or not the vehicle has entered a specific area that is set with respect to the fork;
(g) determining the road on which the vehicle is traveling after passing the fork or on which the vehicle is going to travel after passing the fork, the determination being made based on the detection results and the predetermined conditions relating to the fork; and
(h) correcting the vehicle""s position displayed on the digital road map based on the determined road to match the vehicle""s location on the road to its position on the digital road map.
These and other objects, structures and advantages of the present invention will be apparent more clearly from the following description of the invention based on the examples.